Compound semiconductor device and method of manufacturing the same
A compound semiconductor device includes: a semiconductor substrate; a channel layer over the semiconductor substrate; a carrier supply layer over the channel layer; and a gate electrode, a source electrode and a drain electrode above the carrier supply layer. The semiconductor substrate includes an impurity-containing region containing an impurity, the impurity forms a level lower than a lower edge of a conduction band of silicon by 0.25 eV or more, the impurity forms the level higher than an upper edge of a valence band of silicon.
1. A method of manufacturing a compound semiconductor device comprising:
forming an impurity-containing region containing impurities in a semiconductor substrate, the impurities being Fe, C, Au, or Mg, or combination thereof;
forming an initial layer containing AlN over the semiconductor substrate;
forming a channel layer over the initial layer;
forming a carrier supply layer over the channel layer; and
forming a gate electrode, a source electrode and a drain electrode over the carrier supply layer.
2. The method according to claim 1 , wherein the semiconductor substrate is a silicon substrate or a silicon carbide substrate.
3. The method according to claim 1 , wherein a level of the impurities is higher than an upper edge of a valence band of silicon by 0.25 eV or more.
4. The method according to claim 1 , wherein a level of the impurities is lower than a lower edge of a conduction band of silicon by 0.25 eV or more, the level of the impurities being higher than an upper edge of a valence band of silicon.
5. The method according to claim 1 , further comprising forming a buffer layer containing AlGaN between the semiconductor substrate and the channel layer.
6. The method according to claim 5 , wherein the buffer layer is formed over an initial layer containing AlN, the initial layer formed between the semiconductor substrate and the channel layer.
7. The method according to claim 1 , further comprising forming a superlattice buffer layer in which first nitride semiconductor layers and second nitride semiconductor layers are repeatedly stacked.
8. The method according to claim 7 , wherein the superlattice buffer layer is formed over a buffer layer containing AlGaN, the buffer layer formed between the semiconductor substrate and the channel layer.
9. The method according to claim 7 , wherein the first semiconductor layer contains AlN.
10. The method according to claim 9 , wherein a thickness of the first semiconductor layer is 2 nm or less.
11. The method according to claim 7 , wherein the second semiconductor layer contains AlGaN.
12. The method according to claim 7 , wherein the first nitride semiconductor layers and the second nitride semiconductor layers are repeatedly stacked 80 periods in the superlattice buffer layer.
13. The method according to claim 1 , wherein the initial layer contains the impurities.
14. The method according to claim 1 , wherein the impurities exist at an interface between the semiconductor substrate and the initial layer.
15. The method according to claim 1 , wherein an average impurity concentration is 1 ×10 18 cm −3 or more in a region from an upper surface to a depth of 50 nm of the semiconductor substrate.
16. The method according to claim 1 , wherein a carrier life time in the semiconductor substrate is 1 ×10 −9 seconds or less.